1. Field of the Invention
The present invention generally pertains to thermo-photovoltaic (TPV) technology and more particularly to the application of nanotechnology to TPV cells.
2. Background of the Invention
TPV energy conversion is a conversion process from heat differentials to electricity via photons. A basic thermophotovoltaic system is comprised of a thermal emitter and a photovoltaic diode cell. The temperature of the thermal emitter can vary and, in principle, TPV devices can extract energy from any emitter with temperature elevated above that of the photovoltaic device (forming an optical to electricity engine). The emitter can be a piece of solid material or a specially engineered structure. A conventional solar cell is effectively a TPV device in which the sun functions as the emitter. Thermal emission is the spontaneous emission of photons related to the thermal motion of charges in the material. For normal TPV temperatures, this radiation is mostly at near infrared and infrared frequencies. The photovoltaic diodes can absorb some of these radiated photons and convert them into free charge carriers, that is electricity.
Thermophotovoltaic systems have few, if any, moving parts and are therefore very quiet and require low maintenance. These properties make thermophotovoltaic systems suitable for remote-site and portable electricity-generating applications. Their efficiency-cost properties, however, are often rather poor compared to other electricity-generating technologies.
Carbon nanotubes (CNTS) are an allotrope of carbon. They take the form of cylindrical carbon molecules and have novel properties that make them potentially useful in a wide variety of applications in nanotechnology, electronics, optics and other fields of materials science. They exhibit extraordinary strength and unique electrical properties, and are efficient conductors of heat. Carbon nanotubes and other inorganic nanowires have also been synthesized.
Nanotubes are members of the fullerene structural family, which also includes buckyballs. Whereas buckyballs are spherical in shape, a nanotube is cylindrical, with at least one end typically capped with a hemisphere of the buckyball structure. Their name is derived from their size, since the diameter of a nanotube is on the order of a few nanometers (approximately 50,000 times smaller than the width of a human hair), while they can be up to several millimeters in length. There are two main types of nanotubes: single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs).
Currently, TPV cells are generally based on the traditional semiconductor thin film technology. For a radiation source temperature of 1500K, a cell efficiency of roughly 20% is obtained when the TPV cells operate at room temperature. However, TPV efficiency degrades greatly with increasing cell operating temperature. Currently, it is difficult to obtain efficiency over 30% with the cell temperature of 400K for space power conversion. On the other hand, a low cost TPV having commercial applicability is of great interest.
Therefore, what is needed is a low-cost TPV with a greater cell efficiency that overcomes many of the challenges found in the art, some of which are described above.